Radio shielded spark plug



Dec. 1, 1942. H. RABEZZANA 2,303,389

RADIO SHIELDED SPARK PLUG Filed NOV. 17, 1941 IIIIIHUy Smoentor PatentedDec. l, E942 UNIT aspro smettono seams rape Elector Rabezzana. Flint,Mich., assigner to Ellen'-v eral Motors Corporation, etroit, Mola, acorporation of Delaware Application November 17, i941, Serial No.l19,371 4 canas (ci. 12a- 169) My invention relates to radio shieldedspark plugs designed to prevent high voltage oscillating or varyingcurrent; supplied to the plug by a supply conductor leading thereto,from interfering with the proper operation of radio and like ap-1paratus located adjacent an internal combustion Aengine having anignition system of which my improved shielded plug forms a part; and theobject of my invention is to provide an improved metallic shield devicedesigned to enclose a spark plug made up of features heretofore known,and

which are themselves not claimed herein. This metallic shield is tubularin form and is grounded to the engine through the plug because ofmetalto-metal contact between them, and the iact that the hollow shellof the plug has an externally threaded portion adapted to screw into anopening in the engine cylinder. The tubular metallic shield is commonlythreaded at its upper end to f drawing:

Figure l is a view, much enlarged, showing my improved radio shieldedspark plug upon a een.n trai vertical plane; the conventional spark plugportion thereof being shown in elevation.

Figure 2 is a view showing a section upon a transverse plane indicatedby the line 2 2, Figure 1,1ooking down. A,

Figure 3 is a View showing an externally threaded annular sleeve of myinvention in perspective.

Referring now to the drawing, the spark` plug part of my invention is ormay be of well known or conventional form; and comprises a hollowmetallic shell or casing 5 threaded at its lower end,

-as indicated by the numeral 6, and adapted to screw into a threadedopening in the cylinder or cylinder head of an internal combustionengine.

Within this shell is the usual insulating member 'l of porcelainequivalent material, which is held in place within the shell in any wayas by means of an inturned flange 8 integral with the shell, and whichflange lies above an upper shoulder upon the insulating member l; theinsulating member having another and lower shoulder which rests upon aledge within the shell. Suitable gaskets are provided to insure gastightness as the shield and the spark plug portion.

is usual in spark plugs. The upper end portion of the shell 5 isenlargedto facilitate the holding of the plug per se in assembled relationwithin the lower end of a tubular metallic shield il of my invention, asexemplied by a hexagonal portion lil of the shell; and the upper end ofthe tubular shield is commonly threaded, as at li, so that a metallicconduit through which the conductor which supplies electricity to theplug extends. t hexagonal portion IZ is provided so that my improvedVradio shielded spark plug, comprising the shield 9, the spark plug perse and other ele ments as will hereinafter appear, may be conven-1iently screwed into and removed from a threaded opening in an internalcombustion engine headD The lower end of the shield Q is internallythreaded, as shown, and an abutment is provided adjacent said lower endwhich may be of any suitable form but is shown as comprising an intermalledge I3, and a washer M contacting with said ledge; 'the purpose ofsaid abutment being to provide a stop for and to position the spark:plug within the lower end of the shield because of engagement betweenthe inturned flange d, which is integral with the hollow shell or casing5, and the said abutment.

The numeral l5 designates an externaliy threaded annular sleeve whichsurrounds the shell 5 and is in threaded engagement with the internallythreaded lower end oi the shield t, and the upper end of which sleeveengages with the enlarged upper end portion of the shell and acts toforce the upper end oi the plug per se against the abutment aforesaid,shown as provided by the ledge i3 and the washer it; said sleeve beingshown as having a hexagonal recess i6 at its upper end within which thelower end of `the hexagonal portion I0 of the shell lies when the partsare assembled, as shown in Figure i, and which causes the shield 9 andshell or casing 5 to rotate together as the assembled radio shieldedspark plug is screwed into or unscrewed from the opening provided for itin the engine cylinder. The lower end of the sleeve l has a notchediiange l1 which provides for the use oi a Spanner wrench in assemblingthe parts; and inasmuch as there is metal-to-metal contact between theshield 9 and the shell or casing E, and between said casing and theopening provided for it in the engine cylinder, it follows that when inuse my improved radio shielded spark plug is grounded to the engine withwhich it is used.

The numeral i8 indicates a tubular lining member made of porcelain orequivalent insulat ing material, and the lower end of 'which abuisagainst the washer il when the parts aforesaid are assembled, saidmetallic shield having an inwardly extending ange I9 disposed above theupper end of the lining i8 in the. assembled device; and a resilientwasher 2l is preferably interposed between the upper end of the liningmember I8 and the ilange l! as shown.

In order that the threaded lower end i of the casing 5 of the spark plugpart of my invention will become properly seated in the internallythreaded opening provided for it in the cylinder or cylinder head whenmy invention is installed the length of the sleeve l5, see Figure 1, issuch that the lower end thereof (the under side oi.' the :dange i1 inthe form herein disclosed) will not abut against the upper surface ofthe head before the threaded lower end is properly seated within saidopening; as if the length of said sleeve is such that the lower endthereof abuts against the cylinder head before the threaded lower end isproperly seated there might be leakage of gas from within the cylinderalong the thread. Preferably, and as shown, said sleeve I5 is suicientlyshort that its lower end (or the under side of the ilange l1) lies wellabove the upper surface of the cylinder head when the plug is screwedthereinto.

Having thus described and explained my invention I claim and desire tosecure by Letters Patentz l. In combination with a spark plug having ahollow shell threaded at its lower end to screw into an opening in aninternal combustion en- "gine cylinder, a hexagonal upper portion, and

means at lts upper end for holding an insulating member in placetherein; an externally threaded annular sleeve surrounding said shelland the upper end of which abuts against the lower end of the hexagonalportion thereof; and a tubular metallic shield internally threaded atits lower end in vengagement with said externally threaded annularsleeve, and having an internal member which abuts against the upper endof said spar plugshell.4` ,g l i, 2. In combination with a spark plughaving a hollow shell threaded at its lower end to screw into an openingin an internal combustion engine cylinder, a hexagonal upper portion,and an inturned iiange at its upper end adapted to hold an insulatingmember in place within said shell; and externally threaded annularsleeve surrounding said shell, and having a recess at its upper end intowhich the lower end ot the hexagonal portion of said shell enters; atubular metallic shield internally threaded at its lower end and inengagement with said externally threaded an nular sleeve; and an annularwasher held in place within said shield, and which washer abuts againstthe inturned ilange at the upper end of said spark plug shell.

3. In combination with a spark plug having a hollow shell threaded atits lower end to screw into an opening in an internal combustion enginecylinder, a hexagonal upper portion, and in inturned ilange at its upperend adapted to hold an insulating member in place within said shell; anexternally threaded annular sleeve surrounding said shell, and having arecess at its upper end into which the lower end of the hexagonal por-'tion of said shell enters; -a tubular metallic shield internallythreaded at its lower end and in engagement with said externallythreaded annular sleeve, and which shield has an internal annularshoulder adjacent its lower end, and anA inwardly extending flange atits upper end; an annular washer abutting against said internal shoulderand against the inturned ilange at the upper end of said spark plugshell; a tubular insulating member within said metallic shield and thelower end oi which rests upon said annular washer; and resilient meansbetween said inwardly extending iiange and the upper end of saidinsulating member.

4., In combination with a spark plugY having a hollow metallic shellthreaded at its lower end to screw into an opening in an internalcombustion engine cylinder, an enlarged upper end portion, and means atits upper end for holding an insulating member in place within saidshell; an externally threaded annular sleeve surrounding said shell andthe upper end of which engages the' enlarged upper end portion thereof;a tubular metallic shield internally threaded at its lower end and inengagement with said externally threaded sleeve: and an abutmentadjacent the lower end of said shield, and which abutment engages withthe upper end oi' said spark plug shell.

v HECTOR RABEAZZANA.

